In recent years, many attempts have been made to produce biodegradable molded articles. Among the various materials proposed for producing such articles, the starches are certainly the most desirable since they are cheap, natural products which are very abundant in nature and are completely biodegradable.
European Patent Application No. EP-A-304,401 describes a method for the injection-molding of capsules from destructurized starch. The articles produced by this process, however, have poor mechanical properties as well as being very soluble in water.
Unpublished Italian Patent Application No. 41002-A/89 and the corresponding published International Application No. WO 90/10671 describe a method for producing molded articles with improved mechanical properties in which the starch is mixed with an ethylene-acrylic acid copolymer, possibly with the addition of urea and/or ammonia, in an extruder heated to a temperature of between 90.degree. and 150.degree. C. In this method, the water content of the extrusion is brought to less than 6% by weight, preferably less than 2% by weight, and the resulting composition is then extruded at a temperature of between 130.degree. and 160.degree. C.
European Patent Application No. EP-A-0 87 847 describes a process for preparing foamed gelatinized products made of starch by heating granular or pulverized starch in an extruder press at a temperature of from 60.degree. to 220.degree. C in the presence of 10-30% by weight of water and a gas-forming or gas-generating expanding agent. The obtained foamed material has open pores and high water solubility, which make it suitable for use only as packing material for the protection of fragile articles, as a sound-absorbing or thermal-insulating material, or as a foodstuff.